Federated Farmers said farmers and trucking operators must follow animal welfare rules when taking stock to processing works, especially as drought conditions reduced animal feed in some parts of the country.
Its animal welfare spokesman Andrew Hoggard said the trucker must keep the animals fed and watered for long-distance transport, and both trucker and farmer were legally responsible for making sure stock was suitable for transport at loading.
"When a farmer wants to transport stock off the property, if there is any doubt about suitability for transport then a vet ought to be consulted before loading. That's the rule and it is a good rule," Mr Hoggard said.
"There's a drought in many parts of the South Island and feed is getting tight as we head into winter. This means farmers have to plan ahead to budget extra feed in, or they need to quit their stock well before they become an animal welfare issue."
He said Federated Farmers welcomed an investigation by MPI and would wait for results before commenting further.
The Facebook post has drawn many comments from people outraged at the treatment of the animals.
"Cruelty plain and simple," Maddy Pottinger wrote.
On the Safe Facebook page, Danielle Patchett wrote: "Poor animals. Cows are such gentle and loving creatures. This is sickening."
Safe executive director Hans Kriek said it was clear from the photo the cows were "far below an acceptable body weight".
"For farmers to claim otherwise is ludicrous. If this photo is seen by our overseas trading partners with the comment that this is deemed normal and acceptable by New Zealand farmers, our international reputation will be damaged and rightly so.
"It is appalling that some farmers let their animals deteriorate to this extent and I hope that the MPI investigation will send a strong message that starving your animals will not be tolerated."
MPI spokesman Jim Flack confirmed a complaint had been made and the ministry was investigating.
He said the ministry could not comment further as the investigation was ongoing and "may, or may not, result in a prosecution".
Mr Flack added that under the Animal Welfare Act, both the owner and the transport operator had a responsibility regarding the animals being "fit for transport".
The SPCA was still being sought for comment.
